Protective barrier, in particular for mountainous places

ABSTRACT

The invention concerns a protective barrier comprising a net installed across a slope. The invention is characterized in that the net is maintained by several supports comprising each a first mast globally pointing downstream and whereof one end is fixed to an anchoring point in the ground and a second upright mast resting on the ground, the two masts intersecting side by side in a specifically selected geometrical configuration, in particular with guy cables installed between the masts.

[0001] The invention relates to a protective barrier of the kind comprising a net installed across a slope to protect property and persons from falling rocks and avalanches.

[0002] The invention relates more particularly to the structure of the supports that hold the net in position across the slope.

[0003] In the mountains, the two major hazards are rock falls and avalanches. Some places at risk can be equipped with structures comprising very strong metal nets installed across the slope and held in position by a plurality of supports anchored to the ground. The imperatives are different according to the nature of the hazard: rock falls or avalanches.

[0004] Barriers protecting against rock falls are designed to intercept falling rocks and to dissipate their kinetic energy. This is achieved by deformation of the net, which usually has expandable meshes. The net is held in position by a plurality of supports spaced along a contour line of the slope. These structures are subjected to concentrated and dynamic loads. Barriers protecting against rock falls are covered by French standard NF P 95-308 which defines the specifications of the structures and classifies their performance.

[0005] The nets are conventionally supported by posts normal to the slope and stayed in the upstream, downstream and lateral directions. The conventional system has the drawback that the supports are extremely vulnerable. Moreover, it is necessary to provide the same number of ground anchor points as there are stays. This makes installation on site costly.

[0006] Published French patent No. 2 622 611 describes a structure in which the supports are downstream of the net and consequently protected from impact by the net itself. The number of ground anchor points is nevertheless large.

[0007] French patent No. 2 712 334 describes a support comprising a post connected to a wide base (generally a tripod) to the periphery of which the bottom ends of the stays are fixed. This reduces the number of anchorages to one per support, but this system requires a heavy base of high inertia that can resist bending stresses.

[0008] On the other hand, barriers protecting against avalanches must be designed not to stop an avalanche but to oppose movements of the mantle of snow that lead to avalanches.

[0009] In other words, the net must oppose the thrust of the snow; it is subjected to a uniform and static load. In this type of structure, the net is inclined in the downstream direction, for example at 30° to the normal to the slope. The supports are spaced along a contour line. There is a post every five meters, for example. Barriers protecting against avalanches are covered by French standard NF P 95-304 which defines the dimensional requirements and the strength of various types of structure.

[0010] Avalanche nets are conventionally supported by stayed posts that are inclined in the upstream direction to the normal to the ground. Adapting the structure described in the U.S. Pat. No. 2,712,334 to provide protection against avalanches by modifying the inclination of the posts to the normal to the slope and modifying the base to provide a bipod structure have also been envisaged.

[0011] Improvement and enlargement of winter sports resorts are leading to the provision of protection against rock falls and snowslides on slopes very close to heavily populated places. There is therefore a need for structures that are more discreet and that integrate more readily into an urban mountain landscape. The proliferation of places to be protected is also leading to the design of structures that are less costly to fabricate and easier to install. From the esthetic point of view, bulky steel structures are less and less tolerable for this kind of application.

[0012] Finally, it is desirable for the same structural members to be usable to build either a barrier to protect against rock falls or an avalanche barrier and for the materials used to harmonize as much as possible with the environment.

[0013] The invention provides a satisfactory response to all of these requirements.

[0014] The invention proposes a protective barrier that is relatively inexpensive to fabricate and to install, in particular because each support has only one anchor point, and that is relatively compact.

[0015] Another object of the invention is to propose a support structure whose geometry can be adapted to either of the required forms of protection (stopping rock falls or stabilizing the mantle of snow), the required configuration being obtained in particular by adjusting the stays.

[0016] Another object of the invention is to propose a structure that is particularly discreet, in particular with regard to the net supports, using as much as possible materials integrating well into the landscape, especially wood.

[0017] The invention provides a protective barrier of the kind comprising a net installed across a slope, said net being held by supports anchored to the ground, which barrier is characterized in that a support includes a first mast pointing generally downstream and one end of which is fixed to ground anchoring means and an upright second mast one end of which is fixed to ground bearing means separate from and downstream of said anchor means, in that said net extends between said anchor means and the top end of said second mast, and in that said two masts cross over side-by-side in a chosen geometrical configuration defined at least by the distance between said anchor means and said bearing means, by said net itself, and by stays installed between said masts.

[0018] The anchor means and the bearing means are separate and the anchor means are on the upstream side of the bearing means.

[0019] In a preferred embodiment, one of the masts includes two spaced parallel posts and the other mast is engaged between the two posts. The mast that comprises two parallel posts is preferably said second mast.

[0020] It is noteworthy that all the stays are installed between the masts of the support, at least one of them being of adjustable length so that the geometrical configuration of the support can be adjusted, and in particular adapted to suit the required type of protection. Thus there can be a bottom stay between said anchor means and said bearing means, a top stay between the free end of said first mast and the top end of said second mast, a downstream stay between said bearing means and the free end of said first mast, and an upstream stay between said anchor means and the top end of said second mast.

[0021] The geometrical configuration of the support is adjusted by more particularly adjusting the length of the downstream stay, which can be fitted with a turnbuckle.

[0022] Said first and second masts advantageously consist of wooden posts, for better integration into the environment.

[0023] The invention will be more clearly understood and other advantages of the invention will become more clearly apparent in the light of the following description of one embodiment of a protective barrier according to the invention, which description is given by way of example only and with reference to the accompanying drawings, in which:

[0024]FIG. 1 is a side view of a protective barrier according to the invention;

[0025]FIG. 2 is a perspective view of one support of said barrier;

[0026]FIG. 3 is a diagram showing a geometrical configuration of the support providing an effective barrier against rock falls;

[0027]FIG. 4 is a diagram showing a geometrical configuration of the support providing an effective barrier against avalanches;

[0028]FIG. 5 is a view analogous to FIG. 1 of a different embodiment; and

[0029] FIGS. 6 to 8 show some of the support members.

[0030] A protective barrier 11 according to the invention includes a net 12 installed across a slope 13 and held by spaced supports 14, preferably installed along a contour line of said slope.

[0031] In the drawings, the net 12 is shown in section in the vicinity of one of the supports and is therefore shown only as a line. It is made up of separate and interleaved closed loop metal meshes, of a type known in the art, which gives it a high capacity for elongation by sliding of the meshes one over the other and deformation thereof. This structure is particularly appropriate for absorbing the kinetic energy of rocks (FIG. 3) rolling down the slope. The structure of the net can be different if the protective barrier is adapted to stabilize the mantle of snow and prevent avalanches (FIG. 4). The points at which the net is attached to the supports are not shown in the drawings.

[0032] The invention relates more particularly to the structure of each support 14, shown in detail in the drawings.

[0033] This kind of support includes a first mast 18, pointing in a generally downstream direction, with an inclination that depends on the site and the type of hazard. One end 19 of the first mast is fixed to ground anchor means 20. If the terrain consists of solid rock, this fixing is obtained by drilling a hole in the rock and setting a stake 21 therein. If the ground is less stable, the “exploded stake” technique described in the U.S. Pat. No. 2,712,334 is preferably used. This technique consists of detonating an explosive cartridge at the bottom of the drill hole to obtain a chamber which is filled with concrete in which the anchor stake is set.

[0034] The support further includes an upright second mast 24, one end 25 of which is fixed to ground bearing means 26 farther down the slope than the anchor means 20. Here the net 12 is attached between said anchor means 20 (or a point in the vicinity thereof) and the top end 28 of said second mast. The net can be attached to other points of the support, however, depending on the required configuration.

[0035] According to one important feature of the invention, the aforementioned two masts 18, 24 cross over side-by-side in a geometrical configuration chosen to be suited to the nature of the hazard (falling rocks or unstable snow mantle).

[0036] To be more precise, in the case of intercepting falling rocks, the support has the geometrical configuration shown in FIG. 3 in which said second mast 24 is close to the vertical, whereas to obtain a protective barrier for preventing avalanches, said second mast 24 is instead perpendicular to the slope 13, as shown in FIG. 4.

[0037] The required geometrical configuration is defined by a plurality of parameters such as the distance between the anchor means 20 and the bearing means 26, the width of the net 12 itself, and the length of the stays installed between the two masts.

[0038] According to another feature of the invention, one of the masts comprises two spaced parallel posts 30 and the other mast is engaged between the two posts.

[0039] In this example, and in a preferred configuration, the mast that comprises two parallel posts 30 is said second mast 24. Note that because all of the stays are installed between the masts, each support requires only one anchor point for its erection.

[0040] For example, there is a bottom stay 34 between said anchor means 20 and said bearing means 26. The length of this stay therefore determines the distance between the anchor means and the bearing means. The support also includes a top stay 36 between the free end of said first mast 18 and the top end 28 of said second mast 24. The support further includes a downstream stay 38 between the bearing means and the free end of said first mast 18. Note that this downstream stay is preferably equipped with a turnbuckle 40 constituting effective means of adjusting the geometrical configuration of the support on site and thereby optimizing the position of the net.

[0041] The support can also include an upstream stay 42 between said anchor means 20 and the end 28 of said second mast. This upstream stay can be locally weakened or locally reduced in size to constitute a kind of “fuse” adapted to break on intercepting a rock.

[0042] As a general rule, the relative positions of the two masts 18, 24 depend on the elements indicated hereinabove, i.e. essentially the stays and the net itself. Nevertheless, in some cases, articulating the masts to each other at their crossover point may be envisaged.

[0043]FIG. 5 shows this embodiment, in which an articulation shaft 48 passes through both posts 30 of said second mast 24 and said first mast 18 at a predetermined crossover point. In this case, the upstream stay can be dispensed with.

[0044] The bearing means 26 through which said second mast 24 rests on the ground are described in more detail next with reference to FIGS. 2 and 6. The bearing means include a base 50 consisting simply of a length of U-section laid on the ground, the two parallel branches of the section resting on the ground. Articulation means 52 are formed on the plane top face of the base and carry the bottom end 25 of said second mast. To this end, said articulation means include a yoke 54 attached to the base, a baseplate 56 fixed to the bottom end of said second mast 24 (the baseplate itself carries a yoke on its bottom face), and a shaft 58 providing the articulation between the baseplate and the yoke. The axis of the shaft 58 is substantially parallel to the slope. The ends of the two posts 30 are fixed to the baseplate, on either side of the shaft 58.

[0045] In the example shown, the second mast 24 comprises two wooden posts 30. The two posts are fixed to the baseplate in the following manner. Said baseplate 56 carries two parallel plates 60 engaged in respective central longitudinal slots in the posts.

[0046] Each plate 60 has a hole 61 through it and a transverse rod 62 passes through each post and the corresponding hole. This also defines the distance between the two posts. The top free ends of the two posts 30 are fitted with reinforcements 64. The posts have central longitudinal slots and each of them receives a plate 65 attached to an end disk 66. The plate and the disks that constitute the reinforcement are welded perpendicularly to each other (see FIG. 7). Each plate 65 has a hole 68 through it and a transverse rod 70 passes through each post and the corresponding hole. This also contributes to stabilizing the distance between the posts 30 of said second mast 24.

[0047] The anchor means 20 by means of which one end 19 of said first mast 18 is fixed to the ground are described next with reference to FIGS. 2 and 8. Said anchor means include a base 74 adapted to be fixed to the ground and to which is assembled a disk-shaped baseplate 75 fixed to the upstream end 19 of said first mast 18.

[0048] In the example described, in which the first mast 18 is made of wood, the baseplate of the fixing base is extended by a plate 76 extending along a diameter of the disk and perpendicular thereto, and this plate is engaged in a central longitudinal slot at the upstream end 19 of the first mast. There is a hole 78 through the plate 76 and a transverse rod 80 passes through said first mast 18 and the hole 78. Two annular reinforcements 82 are provided at the two ends of the plate. Each reinforcement surrounds the mast when the plate is engaged in the central longitudinal slot thereof. The fixing base 74 and the baseplate 75 are welded together with an angle between them that depends on the required configuration of the support. The fixing base 74 consists of a length of U-section with a hole 84 through it through which the anchor stake 21 passes.

[0049] The free end of the first mast 18 is also provided with a reinforcement 64 and a transverse rod 86 similar to those at the ends of the two posts 30 of said first mast.

[0050] As previously indicated, the masts are essentially made of wood, for better integration into the environment. The same structure can nevertheless be imagined with metal tubes, or even girders.

[0051] Note further that the ends of the stays terminate in slings passing around the corresponding ends of the masts to which they are attached, the rods 62, 70, 80 and 86 serving as stops. This aligns the forces in the stays with the axial direction relative to the posts constituting the masts.

[0052] It is noteworthy that, in the structure described above, all components operating in bending have been eliminated. Moreover, the single anchor point of the support operates in “pull-out” mode, which is the strongest anchoring mode.

[0053] The ease and accuracy with which the rest position of the net can be adjusted is an important advantage of the structure of the support described above. In particular, note that the angle between the net and a mast in the vicinity of its point of attachment to the latter is large, to define the optimum tension in the net at rest. This angle can easily be adjusted by adjusting the geometry of the support, primarily by adjusting the turnbuckle 40.

[0054] The posts constituting the two masts are preferably machined round timber stock, i.e. have a specific diameter, treated with fungicides and insecticides, for example by impregnating them under pressure with copper salts.

[0055] For avalanche prevention at least, a particularly advantageous configuration is one in which the length of the bottom stay is equal to half the length of the upstream stay and the masts are the same length. In this case, the downstream stay and the top stay are the same length as the bottom stay, which simplifies fabrication.

[0056] The above geometrical characteristics also optimize the distribution of forces in the various parts of the structure and enable standardization of the posts and stays. 

1. A protective barrier of the kind comprising a net (12) installed across a slope, said net being held by supports ( 14) anchored to the ground, which barrier is characterized in that a support includes a first mast (18) pointing generally downstream and one end of which is fixed to ground anchoring means and an upright second mast (24) one end of which is fixed to ground bearing means separate from and downstream of said anchor means, in that said net extends between said anchor means and the top end of said second mast, and in that said two masts (18, 24) cross over side-by-side in a chosen geometrical configuration defined at least by the distance between said anchor means and said bearing means, by said net itself, and by stays installed between said masts.
 2. A protective barrier according to claim 1, characterized in that one of the masts includes two spaced parallel posts (30) and the other mast (18) is engaged between the two posts.
 3. A protective barrier according to claim 2, characterized in that the mast that comprises two parallel posts is said second mast (24).
 4. A protective barrier according to any preceding claim, characterized in that a support includes a bottom stay (34) between said anchor means and said bearing means.
 5. A protective barrier according to any preceding claim, characterized in that a support includes a top stay (36) between the free end of said first mast and the top end of said second mast.
 6. A protective barrier according to any preceding claim, characterized in that a support includes a downstream stay (38) between said bearing means and the free end of said first mast.
 7. A protective barrier according to claim 6, characterized in that said downstream stay is fitted with a turnbuckle (40).
 8. A protective barrier according to any preceding claim, characterized in that a support includes an upstream stay (42) between said anchor means and the top end of said second mast.
 9. A protective barrier according to any preceding claim, characterized in that the two masts are mechanically connected at their crossover point by an articulation shaft (48).
 10. A protective barrier according to any preceding claim, characterized in that said bearing means include a base (50) on which are provided articulation means carrying the bottom end of said second mast.
 11. A protective barrier according to claim 10, characterized in that said articulation means include a yoke (54) attached to said base, a baseplate (56) fixed to the bottom end of said second mast, and a shaft (58) by means of which said yoke and said base are articulated, the axis of said shaft being substantially parallel to the slope.
 12. A protective barrier according to the combination of claim 3 and claim 11, characterized in that the ends of the two posts are mounted on said baseplate (56), on opposite sides of said shaft.
 13. A protective barrier according to any preceding claim, characterized in that said anchor means include a ground fixing base (74) to which is assembled a baseplate (75) fixed to the upstream end of said first mast.
 14. A protective barrier according to claim 13, characterized in that said first mast is made of wood and the baseplate (75) of the fixing base is extended by a plate (76) engaged in a central longitudinal slot of said first mast, in that said plate has a hole through it, and in that a transverse rod (80) passes through said mast and said hole.
 15. A protective barrier according to claim 14, characterized in that the end of said plate opposite said baseplate has an annular reinforcement (82) around said mast.
 16. A protective barrier according to claim 11 or claim 12, characterized in that said second mast consists of two wooden posts and said baseplate includes two parallel plates (60) engaged in respective central longitudinal slots in said posts, in that each plate has a hole (61) through it, and in that a transverse rod (70) passes through each post and the corresponding hole.
 17. A protective barrier according to any preceding claim, characterized in that the ends of a stay 34, 36, 38, 42) are conformed as slings respectively passed around corresponding ends of said masts to which they are attached.
 18. A protective barrier according to the combination of claim 6 and claim 8, characterized in that the masts are substantially the same length and the length of said bottom stay is equal to half the length of said upstream stay. 